1. Field of the Invention
This invention relates to a drive device for a stepping motor such as small-sized stepping motor for use in, for example, diaphragm drive, focusing drive, or the like in a camera.
2. Description of the Prior Art
In the conventional device of this kind, means have been provided for preventing the stepping motor from operating out of balance by varying the amount of power to be applied to the stepping motor when it starts to rotate, or stops from rotation, or employing such an acceleration-deceleration pattern that at the time of starting, it varies from a low to a high value, and at the time of stopping, from the high to the low value.
Also, though such an acceleration-deceleration pattern is effective in the case of a larger number of drive steps then the prescribed value, it is not always effective when the number of drive steps is smaller than the prescribed value. In such a latter case, another driving method, for example, 1-2 phase excitation method, which performs the driving at a low speed with a low possibility of occurrence of faulty operation, has often been employed.
However, in the above-described drive method there was a problem that when the number of drive steps is smaller than the prescribed value, a sufficiently high speed driving could not be obtained.
Such a problem has become very serious particularly when the stepping motor is used as the drive means for the diaphragm of the camera, or the focus control of the photographic lens thereof.